SERVER-131892 made ReplSetTest.initiate() force a checkpoint past the FCV transition, so that a node running an older binary that joins a set declared mixed-version up front cannot initial sync a checkpoint predating that transition.

Tests that perform their own mixed-version setup were missed. They start an all-latest set, run setFeatureCompatibilityVersion to the downgrade FCV themselves, and only then add a node on older binary + reInitiate(). The new node initial syncs its sync source's last checkpoint; if that checkpoint predates the FCV transition, the new node observes an FCV state its binary cannot interpret and fails early in initial sync. The set then never reaches a healthy state and the test times out.